I didn't find any information about this yet. Does every forum user count as a bitrix user regarding included licenses? If the self hosted version has 25 users ... do only they have access to the forum or is a forum user kind of an external or extranet user?

Hi Vaci, Here is the information I found out: There are two types of groups: intranet groups and extranet groups. Each group has its own forum (or discussion). Intranet users can participate in extranet groups (but not the other way round). So you should consider only the number of your intranet users in forums.